Experimental generation and analysis of chaos-modulated pulses for pulsed chaos lidar applications based on gain-switched semiconductor lasers subject to optical feedback.

We experimentally generate and analyze chaos-modulated pulses for pulsed chaos lidar applications based on gain-switched semiconductor lasers subject to optical feedback. While conventional pulsed lidars emit repetitive short pulses without specificity making them vulnerable to interference and range ambiguity, chaos lidars possess the advantages of having no range ambiguity and being immune to interference and jamming, which are benefits of the aperiodic and uncorrelated waveforms we use. Compared to the cw chaos lidars originally proposed, the pulsed chaos lidars can have significantly higher peak power under the class-1 eye-safe regulation that is essential for long-range low-reflectivity target detection. We investigate the temporal, spectral, and cross-correlation characteristics of the modulated pulses obtained with different feedback strengths and modulation currents. Induced by the transient response and evolving with the delayed feedback, modulated pulses exhibiting periodic oscillations and complex dynamics such as chaos are observed. Under a weakly damped condition with large modulation current and moderate feedback strength, we successfully generate uncorrelated chaos-modulated pulses suitable for the pulsed chaos lidar applications. With the current configuration, for cross-correlations comparable to the benchmark of 0.19 set by the cross-correlation of the intensity fluctuation on the sole gain-switched pulses without feedback, uncorrelated waveforms with durations up to 218 ns in a 500 ns modulated pulse can be effectively utilized.

3D pulsed chaos lidar system.

We develop an unprecedented 3D pulsed chaos lidar system for potential intelligent machinery applications. Benefited from the random nature of the chaos, conventional CW chaos lidars already possess excellent anti-jamming and anti-interference capabilities and have no range ambiguity. In our system, we further employ self-homodyning and time gating to generate a pulsed homodyned chaos to boost the energy-utilization efficiency. Compared to the original chaos, we show that the pulsed homodyned chaos improves the detection SNR by more than 20 dB. With a sampling rate of just 1.25 GS/s that has a native sampling spacing of 12 cm, we successfully achieve millimeter-level accuracy and precision in ranging. Compared with two commercial lidars tested side-by-side, namely the pulsed Spectroscan and the random-modulation continuous-wave Lidar-lite, the pulsed chaos lidar that is in compliance with the class-1 eye-safe regulation shows significantly better precision and a much longer detection range up to 100 m. Moreover, by employing a 2-axis MEMS mirror for active laser scanning, we also demonstrate real-time 3D imaging with errors of less than 4 mm in depth.